Bump color-string from 1.5.4 to 1.6.0 in /varfish/vueapp

Bumps [color-string](https://github.com/Qix-/color-string) from 1.5.4 to 1.6.0.
- [Release notes](https://github.com/Qix-/color-string/releases)
- [Changelog](https://github.com/Qix-/color-string/blob/master/CHANGELOG.md)
- [Commits](Qix-/color-string@1.5.4...1.6.0)

---
updated-dependencies:
- dependency-name: color-string
  dependency-type: indirect
...

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